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Community and Q&A

Basement finish floor, slab on grade

Sean Cotter | Posted in General Questions on

With the help of this site I insulated and framed my basement (90 year old house, 8-9″ concrete walls). I did 2 inches of XPS (EPS in hindsight would have been greener but I had a deal on some XPS), 2x framing with Roxul R-15 in between 2x. Rock is next and then floors.

The floor is slab on grade, 3-5″ thick (from what I can tell). Some hairline cracks – very fine. No buckling. Because of how the basement was used before, the floor has a slope from the outer edges to the one corner (laundry). It’s barely noticeable walking on it, not worth losing headroom (+time +cost) pouring self leveling or tearing it up to pour it again. The total area is around 900 sq. ft. but I have a finished laundry and bath + storage area as well as as the utility area that I am not changing the floors in (yet anyway).

The plastic taped to the concrete floor test showed no issues. When it was in the low 20s outside I set up some thermostats and the floor temp was between 50-60 (warmer towards interior), which with all the ducts closed off down there and not much activity other then laundry several times a week, seemed OK.

I don’t like the idea of carpet. If we do have water issues tearing it up is a pain, plus we’ll be using the area (media/family room and spare bedroom) frequently and I want durable. I like the idea of ceramic tile or stone (?) but I am concerned about it being cold on little feet. Big feet too. I live in an old part of town and lots of basements are finished, but if they are cold and unwelcoming they just don’t get used much. I want to avoid that.

So I did some searching and came up a plan of:
Clean and prep concrete
Apply CeraZorb synthetic cork (or other material?) to concrete
Apply electric heating mats/wire in key areas
Lay down tile or stone or brick veneer product (found some online that looks cool)

The actual heated floor area would be small and wouldn’t be the primary source of heat (gas forced air). It would be for comfort mostly.

Has anyone had experience with anything like this? I assume the cork would provide a bit of a thermal break from the concrete? Doing something like or would me to work with the level of the floor and get an old time look. The road outside our house had trolleys at one point and has brick pavers as the surface. The house is brick as well.

My biggest concern is that we would really need to keep the floors on all the time to beat the concrete’s temp.

Any comments on this build up?


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  1. GBA Editor
    Martin Holladay | | #1

    You can't install ceramic tile or stone tile over cork.

    You can install ceramic tile or stone directly to the concrete, but I don't recommend it. You might end up with condensation on the floor during the summer. Any cardboard boxes that you put on the floor might end up with damp bottoms.

    The best approach is always to start with a layer of rigid foam. One inch is better than nothing, by 2 inches of rigid foam is better. Then install a layer of 3/4-inch plywood, screwed through the rigid foam to the concrete below. (Use TapCon screws.)

    Once you've done this work, you can install almost any type of finish flooring you want.

  2. Sean Cotter | | #2

    Thanks Martin.

    Looking at the website for the synthetic cork it looks like it's meant to go under tile - but perhaps that's not suitable for slab on grade?

    At this point (its been 5 years since I purchased the home) I haven't had any trouble with condensation, soggy bottomed boxes, etc. A portion of the basement has tile directly on the slab and we have stored material there with no issues. Overall, the basement does not have a damp feel, even when the humidity is higher.

    My preference would be to insulated with rigid foam and do the plywood method - but head height (as seems to be the case a lot of the time) is limited and the tile approach was the thinnest approach.

    Other options I looked into was Delta then covered with laminate.

    Or, just having a local company smooth the concrete and may do a stain or something and using carpet tiles and throws strategically.

  3. GBA Editor
    Martin Holladay | | #3

    I stand corrected about CeraZorb. I'm not familiar with the product, and I was speaking out of ignorance.

    Your basement floor sounds dry, so you should go ahead with your plan.

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